Orthomyxo- / Paramyxoviruses

Question 1

Orthomyxovirus (influenza)

Answer 1

Key:

• negative enveloped segmented ssRNA virus
• RdRp contained within virion
• attachment HA -> sialic acid on glyco-lipid/protein. NA cleaves sialic acid for release.
• endocytotic penetration, M2 mediated acidicfication uncoating
• *only RNA virus with nucleus replication
• aerosolized droplets, primary replication in epithlium of upper airway -> damaged ciliated respiratory epithelia -> bacterial attachment/invasion (pneumonia)
• rapid onset high fever, myalgia, sore throat, cough
• antigenic shift causes pandemics
• pandemic require: novel HA/NA types (no immunity), human -> human spread, high virulence

Extra:

• Types A & B cause most infection
• contain membrane glycoproteins HA/NA- hemagglutinin & neuroaminidase
• matrix protein M
• HA -> sialic acid is low affinity binding
• needs to transcribe a positive-sense mRNA for translation (not necessary for positive-ssRNA viruses)
• nucleus transcription, cytoplasm translation, nucleus replication, cell membrane assembly/budding
• cytoplasmic translation
• *symptoms caused by IFN
• CTL dependent termination
• viral diversity through antigenic drift (error-prone RdRp) and antigenic shift (segment genome reassortment)
• yearly vaccines: short incubation, lack of virema (weak induction of memory cells), antigen variation

Question 2

Paramyxovirus (general)

Answer 2

• spherical, enveloped negative ss-RNA
• localized: RSV, MPV/HMPV. systemic: measles, mumps
• surface glycoproteins: hemagluttin (HN) & F (fusion)
• *Fusion protein -> cell membrane entrance and cell-cell fusion (synctia), don’t need endosome
• RdRp contained virion, synthesizes positive mRNA
• no nucleus involvement
• plasma membrane assembly and budding

Question 3

Respiratory Synctial Virus (RSV)

Answer 3

Key:

• *nosocomial infant wheezing bronchiolitis & pneumonia during winter
• reinfection is the rule!
• large droplet, fomite, contact transmission
• limited patholgoy to respiratory tract -> epithelial necrosis, airway obstruction: mucous, edema, bronchospasm
• antibody mediated (CD8 weak)

Extra:

• spectrum of mild cold to severe pneumonia
• 3-5 day incubation, fever, cough, SOB
• typical chronic upper tract reinfection since IgA is short-lived (IgG is long-lived in lower respiratory tract)

Question 4

Parainfluenza virus (PIV)

Answer 4

• *toddler croup (laryngotracheobronchitis
• barking cough, stridor, hoarseness

Question 5

Measles

Answer 5

Key:

• aerosol transmission, peaks during prodromal pre-rash
• highly contagious
• nasopharynx replication -> primary viremia -> lymph replication -> secondary viremia -> dissemination
• *3Cs (progressive) cough, coryza, conjunctivitis
• Koplik’s spots (enantham), exanthem (head -> inferior)
• Vitamin A tx

Extra:

• can cause viral or bacterial pneumonia, encephalitis
• lifelong natural immunity (IgG, long incubation, T cell immunity, low antigenic vriation)
• live-atttenuated vaccine
• refuted autism
• Rule out flu & RSV, not clinically distinguishable